Vapor generating system and method

ABSTRACT

A vapor generating system and method in which a heat exchange fluid is selectively exposed to a fluidized bed of relatively low grade fuel to heat the fluid after which it is transferred to a steam drum of a primary boiler for further treatment.

United States Patent 1 1 1111 3,884,193

Bryers May 20, 1975 [54] VAPOR GENERATING SYSTEM AND 3,118,429 Hoczmutlll 1257 3,314,231 1 H mut l2 7 METHOD 3,431,892 3/1969 Godel 122/4 Inventor: Richard ry s, Cranford, J 3,664,307 5/1972 Rowdon, Jr 122/7 [73] Assignee: Foster Wheeler Corporation,

Livin ston, NJ, Primary Examiner-Kenneth W. Sprague Attorney, Agent, or FirmMarvin A. Naigur; John E. [22] Flled' 1974 Wilson; Warren B. Kice [21] Appl. No.: 453,899

[57] ABSTRACT [22] 122/4Fl )2;2L2g0l3 A vapor generating System and method in which a 110/28 J heat exchange fluid is selectively exposed to a fluid- 1 1e 0 can: ized bed of relatively low grade fuel to heat the fluid after which it is transferred to a steam drum of a pri- [56] uNlTE g s giz lis giiENTs mary boiler for further treatment. 2,853,455 9/1958 Campbell et a1 122 4 D 12 Claims 1 Drawing Figure 76 I8 SUPERHEATER wur as 112, 18 I DUST AIR 0011501011 5 HEATER 84 L l0 FUELIN STEAM 1011011512 u I so, f

m L m 38 VAPOR GENERATING SYSTEM AND METHOD BACKGROUND OF THE INVENTION This invention relates to a vapor generating system and method and, more particularly, to such a system and method in which a relatively low grade fuel is burned in a secondary fluidized bed to heat a heat exchange medium which is then routed to a primary boiler for further processing.

Refuse boilers, or boilers operating with a relatively low grade fuel such as waste materials including woodbark and the like, have previously been utilized in connection with modern power plants incorporating one or more conventional type boilers as a means of disposing waste and at the same time, generating energy for production of process steam or electricity.

However, several operational problems exist in burning refuse in a standard boiler due to the high moisture or ash in the fuel. For example, at the relatively high gas temperature and velocities encountered in a con ventional boiler, there is insufficient residence time to complete combustion of fine particles that become entrained in the flue gas. This results in an emissions problem and loss in boiler efficiency.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a fluidized bed refuse fired boiler connected in a power plant which operates in a manner compatible with that of the primary boiler utilized in the power plant.

It is a further object of the present invention to provide a vapor generating system in which a refuse fired fluidized bed boiler is employed which has a fluid circuit connected to the fluid circuit of the primary boiler.

It is a still further object of the present invention to provide a vapor generating system including a refuse fired fluidized bed boiler to burn unspent combustibles collected from the flue gas emitted from the primary boiler at relatively low temperatures and relatively low gas velocities.

Toward the fulfillment of these and other objects, the system of the present invention comprises a primary boiler including a furnace, tube means for containing a heat exchange fluid and for selectively exposing said fluid to the heat from said furnace, and collection means for collecting the heated fluid from said tube means; means for continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, additional tube means for containing a heat exchange fluid and for exposing said fluid to the heat from said bed; and means for connecting said additional tube means to said collection means for transferring the heated fluid from said additional tube means to said collecting means.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a partial sectional, partial schematic representation of the vapor generating system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, the reference numeral refers in general to a primary boiler which consists of an enclosure 12 of a refractory or other insulating material having an opening 14 in its front wall. The rear wall, the side walls, and a portion of the front wall of the enclosure 12 are lined with a plurality of vertically extending spaced parallel tubes, shown schematically by the reference numeral 16. Although not shown in the drawings, it is understood that the tubes have longitudinal, external fins which are connected together to form an air tight structure, in a conventional manner. The ends of the tubes 16 register with headers 18 in a manner so that a heat exchange fluid, such as water, can be circulated through the tubes in selected paths. It is understood that a plurality of burners extend through the walls of the enclosure 12 and the tubes 16, and are supplied with hogged fuel in a conventional manner to maintain the boiler 10 at a predetermined operating temperature. Hogged fuel is well known in the art as a woodbark refuse type of fuel. As a result, the temperature of the water is gradually raised by the heat generated in the boiler 10 as the water passes through the tubes 16.

The boiler 10 is provided with a collection drum 20 for steam and water which is connected to the fluid circuit including the tubes 16 and the headers 18 by a line 25. The drum 20 is also connected, via a plurality of tubes 22, to a water or mud drum 24 which, in turn, is connected by a line 26 to the lower headers 18.

A secondary, or refuse boiler, shown generally by the reference numeral 30, is disposed adjacent the primary boiler 10 and is formed by an enclosure 32 of a refractory or other insulating material which is lined with a plurality of finned tubes 34 connected to headers 36 to establish a fluid circuit, similar to that of the boiler 10. Water is directed from a source 37, through a line 38 under the force of a pump 39 into a header 36 for air culation through the tubes 34 and the remaining headers.

A horizontal, perforated air distribution plate 40 is provided in the lower portion of the boiler 30. Air from a forced draft fan 42 is passed through a line 44 and into the lower portion of the boiler 30 through an opening 46 and flows upwardly through the plate 40 as shown by the dashed arrows in the drawing. Particulate material from a source (not shown) is fed into the chamber 30, mixed with the inert material, shown by the reference numeral 52, which is fluidized by the air passing through the plate. The fuel material may be fed into the boiler 30 by pneumatic injection, and provision can be made for supplementary feed and ash removal, all in a conventional manner.

The bed material is an inert material, sized to fluidize at low velocities. It is understood that the velocity and rate of flow of the air passing through the plate 40 and into the bed 52 is regulated so that it is high enough to fluidize the particulate material and obtain good combustion, but low enough to avoid the loss of too many fine fuel particles from the bed.

The hot gases from the fluidized bed 52 pass upwardly in the boiler 30, outwardly through an opening in the top thereof and into a duct 54 which registers with an opening formed in the side of the boiler 10. As a result, the combustion gases from the boiler 30 pass into the boiler 10 and combine with those from the latter boiler, and the resulting mixture passes upwardly through the boiler 10 and exits through the opening 14 as shown by the dashed arrows.

Referring again to the boiler 30, a line connects an upper header 36 to a bank of tubes, shown in general by the reference numeral 62, disposed in the fluidized bed 52, with the outlet of the tubes being connected by a line 64 to the drum 20 of the primary boiler 10. During its passage through the tubes 34, the headers 36, and the bank of tubes 62, the temperature of the water is raised sufficiently to convert at least a portion thereof to steam which enters in the drum 20 of the boiler 10. The steam and water entering the drum 20 from the line 64 and from the line 65 are separated, with the steam being passed to a superheater 66 for further heating and then via a line 70, to another section of the power plant such as a turbine for further use, while the water in the drum 20 is passed, via tubes 22, to the water drum 24 with the water flowing through the tubes 22 being heated by the hot gases exiting from the boiler 10. The water is then routed from the drum 24 via line 26 to the lower headers 18 of the primary boiler, and via line 72 to the water line 38 supplying the tubes 34 of the secondary boiler 30, for further circulation.

The boiler 30 thus can receive water from two sources, i.e. the drum 24 in which case it converts the water to steam, and the source 37 in which case it heats the water to a temperature just below saturation and thus operates as an economizer, or feedwater heater.

The mixture of combustion gases from the primary boiler and the secondary boiler 30 are passed from the outlet 14 of the primary boiler to an air heater 74 which effects a heat exchange with the gases and air from a forced draft fan 76 introduced into the air heater via a line 78. The gases from the air heater 74 are passed through a line 80 into a dust collector 82 where the fine particles entrained in the gases are separated therefrom. The resulting relatively clean gases from the dust collector 82 are passed via a line 84 to a stack 86 for exhausting the gases to atmosphere. The fine solid particles separated from the gases in the dust collector 82 are passed through a line 88 and to a line 90 which is adapted to inject the particles into the fluidized bed 52 in the boiler 30 and thus supplement the fuel supply from the main source.

The heated air from the air heater 74 passes via a line 92 to the line 90 before entering the bed 52.

The use of a fluidized bed for the low grade fuel enables the boiler 30 to be operated at a relatively low temperature and thus minimize slagging, while enabling a relatively small bed volume to be used. Also, lower gas velocities can be used in the boiler 30 which permits a longer residence time to ensure complete combustion of the waste material. As a result, low grade waste material, such as woodbark, or the life, can be used to improve the overall efficiency of the power plant.

Of course, other variations of the specific construction and arrangement of the vapor generating system and method disclosed above can be made by those skilled in the art without departing from the invention as defined in the appended claims.

What is claimed is:

l. A vapor generating system comprising a primary boiler including a furnace, tube means for containing a heat exchange fluid and for selectively exposing said fluid to the heat from said furnace, and collection means for collecting the heated fluid from said tube means; means for continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace; additional tube means for containing a heat exchange fluid and for exposing said fluid to the heat from said bed; means for connecting said additional tube means to said collection means for transferring the heated fluid from said additional tube means to said collecting means; means for passing the combustion gases from said fluidized bed into said furnace where they combine with the combustion gases from said furnace, whereby heat recovery is provided from the fluidized bed combustion gases directly to the primary boiler; means for separating the solid particles from the combustion gases leaving said primary boiler; and means for passing said particles into said fluidized bed.

2. The system of claim 1 wherein said collection means is adapted to separate that portion of said fluid in a vapor state from that portion of fluid in a liquid state.

3. The system of claim 2 further comprising means for passing a portion of the liquid portion of said fluid back to said additional tube means.

4. The system of claim 2 further comprising means for passing a portion of the liquid portion of said fluid back to said tube means of said primary boiler.

5. A method for generating vapor comprising the steps of passing a heat exchange fluid through a plurality of tubes in a heat exchange relation to a furnace, collecting the heated fluid from said tubes in a drum, continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, passing heat exchange fluid through additional tubes in a heat exchange relation to said fluidized bed; transferring the heated fluid from said additional tubes to said drum; passing the combustion gases from said fluidized bed into said furnace where they combine with the combustion gases from said furnace; separating the solid particles from the combustion gases leaving said furnace; and passing said particles into said fluidized bed.

6. The method of claim 5 further comprising the step of separating that portion of said fluid in a vapor state from that portion of fluid in a liquid state in said drum.

7. The method of claim 6 further comprising the step of passing a portion of the liquid portion of said fluid back to said additional tubes.

8. The method of claim 6 further comprising the step of passing a portion of the liquid portion of said fluid back to said first tubes.

9. A vapor generating system comprising a primary boiler including a furnace, tube means for containing a heat exchange fluid and for selectively exposing said fluid to the heat from said furnace, and collection means for collecting the heated fluid from said tube means; a secondary boiler including means for continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, and additional tube means for containing a heat exchange fluid and for exposing said fluid to the heat from said bed; means for connecting said additional tube means to said collection means for transferring the heated fluid from said additional tube means to said collecting means; and means for passing the combustion gases from said secondary boiler into said primary boiler where they combine with the combustion gases from said furnace.

10. The system of claim 9 wherein said collection means is adapted to separate that portion of said fluid in a vapor state from that portion of fluid in a liquid state, and further comprising means for passing a portion of the liquid portion of said fluid back to said additional tube means, and means for passing another portion of the liquid portion of said fluid back to said tube means of said primary boiler.

11. A method for generating vapor comprising the steps of passing a heat exchange fluid through a plurality of tubes in a heat exchange relation to a furnace, collecting the heated fluid from said tubes in a drum, continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, passing heat exchange fluid through additional tubes in a heat exchange relation to said bed; transferring the heated fluid from said additional tubes to said drum; and pass first tubes. 

1. A vapor generating system comprising a primary boiler including a furnace, tube means for containing a heat exchange fluid and for selectively exposing said fluid to the heat from said furnace, and collection means for collecting the heated fluid from said tube means; means for continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace; additional tube means for containing a heat exchange fluid and for exposing said fluid to the heat from said bed; means for connecting said additional tube means to said collection means for transferring the heated fluid from said additional tube means to said collecting means; means for passing the combustion gases from said fluidized bed into said furnace where they combine with the combustion gases from said furnace, whereby heat recovery is provided from the fluidized bed combustion gases directly to the primary boiler; means for separating the solid particles from the combustion gases leaving said primary boiler; and means for passing said particles into said fluidized bed.
 2. The system of claim 1 wherein said collection means is adapted to separate that portion of said fluid in a vapor state from that portion of fluid in a liquid state.
 3. The system of claim 2 further comprising means for passing a portion of the liquid portion of said fluid back to said additional tube means.
 4. The system of claim 2 further comprising means for passing a portion of the liquid portion of said fluid back to said tube means of said primary boiler.
 5. A method for generating vapor comprising the steps of passing a heat exchange fluid through a plurality of tubes in a heaT exchange relation to a furnace, collecting the heated fluid from said tubes in a drum, continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, passing heat exchange fluid through additional tubes in a heat exchange relation to said fluidized bed; transferring the heated fluid from said additional tubes to said drum; passing the combustion gases from said fluidized bed into said furnace where they combine with the combustion gases from said furnace; separating the solid particles from the combustion gases leaving said furnace; and passing said particles into said fluidized bed.
 6. The method of claim 5 further comprising the step of separating that portion of said fluid in a vapor state from that portion of fluid in a liquid state in said drum.
 7. The method of claim 6 further comprising the step of passing a portion of the liquid portion of said fluid back to said additional tubes.
 8. The method of claim 6 further comprising the step of passing a portion of the liquid portion of said fluid back to said first tubes.
 9. A vapor generating system comprising a primary boiler including a furnace, tube means for containing a heat exchange fluid and for selectively exposing said fluid to the heat from said furnace, and collection means for collecting the heated fluid from said tube means; a secondary boiler including means for continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, and additional tube means for containing a heat exchange fluid and for exposing said fluid to the heat from said bed; means for connecting said additional tube means to said collection means for transferring the heated fluid from said additional tube means to said collecting means; and means for passing the combustion gases from said secondary boiler into said primary boiler where they combine with the combustion gases from said furnace.
 10. The system of claim 9 wherein said collection means is adapted to separate that portion of said fluid in a vapor state from that portion of fluid in a liquid state, and further comprising means for passing a portion of the liquid portion of said fluid back to said additional tube means, and means for passing another portion of the liquid portion of said fluid back to said tube means of said primary boiler.
 11. A method for generating vapor comprising the steps of passing a heat exchange fluid through a plurality of tubes in a heat exchange relation to a furnace, collecting the heated fluid from said tubes in a drum, continuously combusting a fluidized bed of fuel of a lower grade than that used in said furnace, passing heat exchange fluid through additional tubes in a heat exchange relation to said bed; transferring the heated fluid from said additional tubes to said drum; and passing the combustion gases from said bed into said furnace where they combine with the combustion gases from said furnace.
 12. The method of claim 11 further comprising the steps of separating that portion of said fluid in a vapor state from that portion of fluid in a liquid state in said drum, passing a portion of the liquid portion of said fluid back to said additional tubes; and passing another portion of the liquid portion of said fluid back to said first tubes. 